Better styling and sizing of strips.
Detect old common controls and use compatible colours.
Use TransparentBlt to show themed background.
Link to msimg32 system lib for TransparentBlt.
Size check boxes to be square in normal mode and enlarged text mode.
Size incremental search strip to be same height as find strip in enlarged text mode.

Minimize conditional compilation for theming by defining HTHEME when needed.
Drop THEME_STRIPS definition and check for DTBG_CLIPRECT which is defined in
both MingW and Microsoft versions of Uxtheme.h.